1. Field of the Invention
The present invention relates to a liquid ejection apparatus in which switching can easily be performed from a printing state to a cleaning state or a waiting state for a liquid ejection head having formed therein a nozzle row that ejects a liquid.
2. Description of the Related Art
In a liquid ejection apparatus such as an ink jet printer, a liquid is ejected from a nozzle row formed in a liquid ejection head, and an image or the like is formed on a recording sheet. Therefore, if an image or the like is formed while an ink ejection surface of the liquid ejection head from which the liquid is ejected (the portion in which the nozzle row is formed) is dirty, or while a liquid, dirt or the like adheres to the surface, the quality of printing is degraded. Especially, in the case of a full-color ink jet printer, if an ink (a liquid) of a color different from that of another ink flows back through a nozzle into where the latter ink is, the former is mixed with the latter ink and, upon printing, an ink of mixed colors is ejected, which degrades the quality of the image.
Thus, in order to prevent degradation of the quality of printing and maintain the performance of the liquid ejection head, there are various methods for performing head maintenance in accordance with purposes. For example, there is a technique in which a somewhat hard rubber blade is pressed against the ink ejection surface (the liquid ejection surface) of a liquid ejection head and slides on the ink ejection surface to clean the surface. In this rubber-blade method, dirt adhering to the ink ejection surface, an accumulated ink, an ink that has become viscous or solid or the like is wiped off and removed. By performing such wiping, the ink ejection surface is kept clean and a stable performance of ink ejection can be obtained.
There is another head-maintenance technique in which the ink ejection surface of a liquid ejection head is capped so that adhesion of dirt or drying is prevented. Specifically, when the apparatus is in a waiting state, such as when printing is not being performed, a head cap in the form of an upwardly open shallow box is brought into contact with the ink ejection surface to cover the ink ejection surface. As a result, since the interior of the head cap becomes sealed, the ink ejection surface is protected from dust and foreign matter and is not easily dried, so that clogging of the nozzles can be prevented.
There is still another technique in which ink is sucked from the ink-ejection-surface side using a pump while the ink ejection surface is in a capped airtight state, so that dirt and bubbles in the liquid ejection head are forced out together with the liquid. By performing negative-pressure suction in this way, dirt and bubbles, which are a cause of unsuccessful ejection, are removed from inside the liquid ejection head so that a stable performance of ink ejection can be obtained. There is still another technique in which a liquid-absorbing member made of a porous material or the like is provided at the inner bottom portion of a head cap and impregnated with a moisturizing liquid (water, ink or the like), which evaporates and thereby the ink ejection surface is wetted and prevented from drying in an active manner.
Thus, there are head-maintenance techniques in which the ink ejection surface is wiped, capped and so on. However, in order to perform wiping or capping, a mechanism that moves the rubber blade translationally between the ink ejection surface of the liquid ejection head and a printing table, a mechanism that moves the head cap up and down, or the like is necessary. Also, considerations of physical relationships are necessary in order that these head-maintenance operations do not interfere with one another. Therefore, these techniques can lead to increased complexity of the mechanism and increase in the cost or the size of the ink jet printer.
For this reason, there is a technique in which a platen portion, a cap portion, an ink-absorbing portion and a wiper portion are separately arranged on the outer periphery of a rotatable platen unit. In this technique, the platen unit is driven to rotate and slide so as to perform a recording-sheet-supporting operation in a printing state, a wiping operation in a cleaning state and a capping operation in a waiting state. Thus, the space occupied by the head-maintenance mechanism is reduced to make the ink jet printer small.
There is also another technique in which a rotating member is arranged below the liquid ejection head. The rotating member has a head-maintenance portion including a rubber blade, a head cap and the like, and a platen portion in the form of ribs that supports the back side of a recording sheet. In this technique, by rotating the rotating member, switching can be performed between four states of capping (in a waiting state), wiping (in a cleaning state), priming (in a cleaning state) and printing. Therefore, the time necessary for head maintenance can be reduced and, moreover, the head-maintenance mechanism can be simplified.